Dosimetry Check Research Articles

Radiotherapy delivery error detection with electronic portal imaging device (EPID)-based in vivo dosimetry.

Radiotherapy delivery error detection with electronic portal imaging device (EPID)-based in vivo dosimetry.

A Validation Method for EPID In Vivo Dosimetry Algorithms

The aim of this study was to develop and apply an evaluation method for assessing the accuracy of a novel 3D EPID back-projection algorithm for in vivo dosimetry. The novel algorithm of Dosimetry Check (DC) 5.8 was evaluated. A slab phantom homogeneously filled, or with air and bone inserts, was used for fluence reconstruction of different squared fields. VMAT plans in different anatomical sites were delivered on an anthropomorphic phantom. Dose distributions were measured with radiochromic films. The 2D Gamma Agreement Index (GAI) between the DC and the film dose distributions (3%, 3 mm) was computed for assessing the accuracy of the algorithm. GAIs between films and TPS and between DC and TPS were also computed. The fluence reconstruction accuracy was within 2% for all squared fields in the three slabs’ configurations. The GAI between the DC and the film was 92.7% in the prostate, 92.9% in the lung, 96.6% in the head and the neck, and 94.6% in the brain. An evaluation method for assessing the accuracy of a novel EPID algorithm was developed. The DC algorithm was shown to be able to accurately reconstruct doses in all anatomic sites, including the lung. The methodology described in the present study can be applied to any EPID back-projection in vivo algorithm.

Improving dose delivery accuracy with EPID in vivo dosimetry: results from amulticenter study.

To investigate critical aspects and effectiveness of in vivo dosimetry (IVD) tests obtained by an electronic portal imaging device (EPID) in amulticenter and multisystem context. Eight centers with three commercial systems-SoftDiso (SD, Best Medical Italy, Chianciano, Italy), Dosimetry Check (DC, Math Resolution, LCC), and PerFRACTION (PF,Sun Nuclear Corporation, SNC, Melbourne, FL)-collected IVD results for atotal of 2002 patients and 32,276 tests. Data are summarized for IVD software, radiotherapy technique, and anatomical site. Every center reported the number of patients and tests analyzed, and the percentage of tests outside of the tolerance level (OTL%). OTL% was categorized as being due to incorrect patient setup, incorrect use of immobilization devices, incorrect dose computation, anatomical variations, and unknown causes. The three systems use different approaches and customized alert indices, based on local protocols. For Volumetric Modulated Arc Therapy (VMAT) treatments OTL% mean values were up to 8.9% for SD, 18.0% for DC, and 16.0% for PF. Errors due to "anatomical variations" for head and neck were up to 9.0% for SD and DC and 8.0% for PF systems, while for abdomen and pelvis/prostate treatments were up to 9%, 17.0%, and 9.0% for SD, DC, and PF, respectively. The comparison among techniques gave 3% for Stereotactic Body Radiation Therapy, 7.0% (range 4.7-8.9%) for VMAT, 10.4% (range 7.0-12.2%) for Intensity Modulated Radiation Therapy, and 13.2% (range 8.8-21.0%) for 3D Conformal Radiation Therapy. The results obtained with different IVD software and among centers were consistent and showed an acceptable homogeneity. EPID IVD was effective in intercepting important errors.

EPID-based 3D dosimetry for pre-treatment FFF VMAT stereotactic body radiotherapy plan verification using dosimetry CheckTM.

The software Dosimetry Check (DC) reconstructs the 3D dose distribution on CT images data set by using EPID measured signal. This study aimed to evaluate DC for stereotactic body radiotherapy (SBRT) with unflattened photon beams (FFF) for dosimetric independent plan verification in pre-treatment modality. DC v.4.1 was configured for Varian TrueBeam STx FFF beams equipped with EPID aS-1200. The DC FFF models were tested using arc open fields (from 1×1cm2 to 15×15cm2) and VMAT (Volumetric Modulated Arc Therapy) SBRT plans on phantom and patient CTs. DC dose distributions (DDC) were compared with that calculated by Eclipse with Acuros XB algorithm (DAXB) and one measured by Octavius 1000 SRS detector (DOCT). All differences were quantified in terms of the local 3D gamma passing rate (%GP), DVH and point dose differences. DC was configured for FFF VMAT using an appropriate correction procedure. %GP2%2mm (mean±standard deviation) of DOCT-DDC was 96.3±2.7% for open fields whereas it was 90.1±5.9% for plans on homogeneous phantom CT. However, average %GP3%3mm of DAXB-DDC was 95.0±4.1 for treatments on patient CT. The fraction of plans passing the %GP3%3mm DQA tolerance level [10% (50%) of maximum dose threshold] were 20/20 (14/20) and 18/20 (16/20) for OCT on phantom CT and DC on patient CT, respectively. DC characterization for FFF beams was performed. For stereotactic VMAT plan verifications DC showed good agreement with TPS whereas underlined discrepancies with Octavius in the high dose regions. A customized tolerance level is required for EPID-based VMAT FFF pre-treatment verification when DC system is applied.

Dosimetric Comparison of Four Commercial Patient-Specific Quality Assurance Devices for Helical Tomotherapy

In this study, the delivery quality assurance (DQA) results of commercially available dosimetric systems (ionization chamber and EBT film, MapCHECK, ArcCHECK, and dosimetry check (DC) software) for helical tomotherapy (HT) were compared, and the feasibility of performing pretreatment using MapCHECK, ArcCHECK, and DC for HT, instead of ionization chambers and EBT films, was assessed. Sixty-five HT-treated patients were considered. Point dose differences, dose profiles, and gamma passing rates were used to evaluate the agreement between the calculated and the measured data, and the outcomes of the four DQA devices were compared in various clinical cases. The calculated and the measured point doses were within ±5% of each other. In terms of the root-mean-square error (RMSE), the point dose differences were within 2.9 for the four tested devices in all of the studied cases. Gamma analysis was performed based on the 3%/3 mm and 2%/2 mm passing rate criteria. In terms of the average RMSE, the gamma passing rates of the four tested DQA devices were within 2.85 (3%/3 mm) and 7.30 (2%/2 mm). These DQA systems could be used interchangeably for routine DQA pretreatment in HT cases.

EP-1748 Adaptive solution for an improved treatment verification using Dosimetry Check system

EP-1748 Adaptive solution for an improved treatment verification using Dosimetry Check system

EPID-based invivo dosimetry using Dosimetry Check™: Overview and clinical experience in a 5-yr study including breast, lung, prostate, and head and neck cancer patients.

BackgroundIndependent verification of the dose delivered by complex radiotherapy can be performed by electronic portal imaging device (EPID) dosimetry. This paper presents 5‐yr EPID in vivo dosimetry (IVD) data obtained using the Dosimetry Check (DC) software on a large cohort including breast, lung, prostate, and head and neck (H&N) cancer patients.Material and MethodsThe difference between in vivo dose measurements obtained by DC and point doses calculated by the Eclipse treatment planning system was obtained on 3795 radiotherapy patients treated with volumetric modulated arc therapy (VMAT) (n = 842) and three‐dimensional conformal radiotherapy (3DCRT) (n = 2953) at 6, 10, and 15 MV. In cases where the dose difference exceeded ±10% further inspection and additional phantom measurements were performed.ResultsThe mean and standard deviation (μ±σ) of the percentage difference in dose obtained by DC and calculated by Eclipse in VMAT was: 0.19±3.89% in brain, 1.54±4.87% in H&N, and 1.23±4.61% in prostate cancer. In 3DCRT, this was 1.79±3.51% in brain, −2.95±5.67% in breast, −1.43±4.38% in bladder, 1.66±4.77% in H&N, 2.60 ± 5.35% in lung and −3.62±4.00% in prostate cancer. A total of 153 plans exceeded the ±10% alert criteria, which included: 88 breast plans accounting for 7.9% of all breast treatments; 28 H&N plans accounting for 4.4% of all H&N treatments; and 12 prostate plans accounting for 3.5% of all prostate treatments. All deviations were found to be as a result of patient‐related anatomical deviations and not from procedural errors.ConclusionsThis preliminary data shows that EPID‐based IVD with DC may not only be useful in detecting errors but has the potential to be used to establish site‐specific dose action levels. The approach is straightforward and has been implemented as a radiographer‐led service with no disruption to the patient and no impact on treatment time.

Characterization of EPID software for VMAT transit dosimetry.

Dosimetry check (DC) is a commercial software that allows reconstruction of 3D dose distributions using transit electronic portal imaging device (EPID) images. In this work, we evaluated the suitability of DC software for volumetric modulated arc therapy (VMAT) transit dosimetry. The volumetric gamma agreement index 3%/3mm between twenty VMAT dose distributions reconstructed by DC and calculated with treatment planning system (TPS) were compared to those obtained using PTW OCTAVIUS®4D to assess DC accuracy in VMAT quality assurance (QA). The sensitivity of DC in detecting VMAT delivery and set-up errors and anatomical variations has been investigated by measuring the variation of the gamma agreement index before and after the introduction of specific errors in four VMAT plans related to different anatomical sites. The influence of dose computation algorithm in presence of density inhomogeneity was also assessed. The assessment of VMAT QA shows agreements with TPS maps comparable to OCTAVIUS® 4D (OCT) in homogeneous phantom (p < 0.001). DC mean gamma agreement index was 94.2%±3.4, versus 95.6%±2.5 of OCT, lower dose threshold was set to 10%. Introduction of deliberate errors resulted in lower gamma agreement index and in 38/56 cases the gamma agreement index was over the detection threshold. The dose computation algorithm of DC is accurate in all anatomical sites except lung. However in lung cases, the aqua vivo approach used in this work reduced the algorithm dependence of DC results. DC accurately reproduced VMAT 3D dose distributions in phantom and is sensitive to detect errors caused by delivery inaccuracy and anatomical variations of patients.

EP-1759: MLC positioning study based on EPID images analyzed with the Dosimetry Check software

EP-1759: MLC positioning study based on EPID images analyzed with the Dosimetry Check software

EPID-based dosimetry using a commercial software: Gamma analysis and DVH metrics for VMAT pre-treatment and in vivo QA

Introduction 3D EPID-based dosimetry can play a key role in the chain of verification procedures in VMAT treatments. Anatomical-based metrics could improve evaluation through meaningful clinical dosimetric parameters both for pre-treatment and in vivo QA. Purpose To evaluate the use of a commercial software to reconstruct dose from EPID measurements for pre-treatment verification and transit dosimetry using 3D patient-based metrics. Materials and methods Dosimetry Check is used for pre-treatment and in vivo 3D evaluations applied to ten VMAT treatments for various anatomical sites (prostate, head & neck, spine and abdomen), planned by Eclipse and delivered by Clinac 2100CD, equipped with a S1000 EPID. Furthermore, for each case, a verification plan is delivered to an homogeneous elliptical shaped solid water phantom to compare in vivo-phantom dose reconstruction and dose measurements by a micro ionization chamber CC01. Results Whole dose grid 3D gamma evaluation is performed with criteria 3%-3 mm and 5%-3 mm. Gamma metrics is applied to specific ROI of interest: PTV, CTV and OARs. DVHs are compared in terms of D2, D98, D50 and OARs constraints values used during planning. Differences between pre-treatment and in vivo reconstructed dose are mostly within 3% (5% in sites with small inhomogeneities). Isodose levels reconstructed from Dosimetry Check in phantom are within 3% compared to absolute dose measured by micro ionization chamber. Conclusion Patient-based metrics can be used to evaluate results in terms of target coverage and OAR constraints, improving QA evaluation for VMAT treatments. Further studies are needed to evaluate action levels for ROI-based gamma evaluation and critical DVH goals.

SU‐E‐T‐379: Evaluation of An EPID‐Based System for Daily Dosimetry Check by Comparison with a Widely‐Used Ionization Chamber‐Based Device

Purpose:To examine the feasibility of using Varian's EPID‐based Machine Performance Check (MPC) system to track daily machine output through comparison with Sun Nuclear's DailyQA3 (DQA) device.Methods:Daily machine outputs for two photon energies (6 and 16MV) and five electron energies (6, 9, 12, 16, 20MeV) were measured for one month using both MPC and DQA. Baselines measurements for MPC were taken at the start of the measurement series, while DQA baselines were set at an earlier date. In order to make absolute comparisons with MPC, all DQA readings were referenced to the average of the first three DQA readings in that series, minimizing systematic differences between the measurement techniques due to baseline differences. In addition to daily output measurements, weekly averages were also calculated and compared. Finally, the electron energy dependence of each measurement technique was examined by comparing energy‐specific measurements to the average electron output of all energies each day.Results:For 6 and 16MV photons, the largest absolute percent differences between MPC and DQA were 0.60% and 0.73%, respectively. Weekly averages were within 0.17% and 0.23%, respectively. For all five electron energies, the greatest absolute percent differences between MPC and DQA for each energy ranged from 0.49%–0.83%. Weekly averages ranged from 0.07%–0.28%. DQA energy‐specific electron readings matched the average electron output within 0.29% for all days and all energies. MPC energy‐specific readings matched the average within 0.21% for 9–20MeV. However, 6MeV showed a larger distribution about the average with four days showing a difference greater than 0.30% and a maximum difference of 0.51%.Conclusion:MPC output measurements correlated well with the widely‐used DQA3 for most beam energies, making it a reliable back up technique for daily output monitoring. However, MPC may display an energy dependence for lower electrons energies, requiring additional investigation.

SU‐E‐T‐62: A Preliminary Experience of Using EPID Transit Dosimetry for Monitoring Daily Dose Variations in Radiation Treatment Delivery

Purpose:To investigate the use of EPID transit dosimetry for monitoring daily dose variations in radiation treatment delivery.Methods:A patient with head and neck cancer treated using nine field IMRT beams was used in this study. The prescription was 45 Gy in 25 fractions. A KV CBCT was acquired before each treatment on a Varian NTX linear accelerator. Integrated images using MV EPID were acquired for each treatment beam. Planning CT images, treatment plan, and daily integrated images were imported into a commercial QA software Dosimetry Check (v4r4 Math Resolutions, LLC, Columbia, MD) to calculate 3D dose of the day assuming 25 fractions treatment. Planning CT images were deformed and registered to each daily CBCT using Varian SmartAdapt (v11.MR2). ROIs were then propagated from planning CT to daily CBCT. The correlation between maximum, average dose of ROIs and ROI volume, center of mass shift, Dice Similarity Coefficient (DSC) were investigated.Results:Not all parameters investigated showed strong correlations. For PTV and CTV, the average dose has inverse correlation with their volume change (correlation coefficient −0.52, −0.50, respectively) and DSC (−0.59, −0.59, respectively). The average dose of right parotid has correlation with its volume change (0.56). The maximum dose of spinal cord has correlation with the center of mass superior‐inferior shift (0.52) and inverse correlation with the center of mass anterior‐posterior shift (−0.73).Conclusion:Transit dosimetry using EPID images collected during treatment delivery offers great potential to monitor daily dose variations due to patient anatomy change, motion, and setup errors in radiation treatment delivery. It can provide a patient‐specific QA tool valuable for adaptive radiation therapy. Further work is needed to validate the technique.

SU‐E‐J‐64: Evaluation of a Commercial EPID‐Based in Vivo Dosimetric System in the Presence of Lung Tissue Heterogeneity

Purpose:To study the performance of Dosimetry Check (DC), an EPID‐based dosimetry software, which allows performing transit dosimetry, in low density medium, by comparing calculations in‐phantom, and analysing results for 15 lung patients.Methods:DC software (v.3.8, pencil beam‐based algorithm) has been tested, for plans (Eclipse v.10.0 TPS) delivered in two Varian Clinac iX equipped with aS1000 EPIDs.In the CIRS lung phantom, comparisons between DC and Eclipse (Acuros) were performed for several plans: (1) four field box; (2) square field delivered in arc mode; (3) RapidArc lung patient plan medially centred; (4) RapidArc lung patient plan centred in one lung. Reference points analysed: P1 (medial point, plans 1–3) and P2 (located inside one lung, plan 4).For fifteen lung patients treated with RapidArc, the isocentre and 9 additional points inside the PTV as well as the gamma passing rate (3%/3mm) for the PTV and at the main planes were studied.Results:In‐phantom:P1: Per‐field differences in plan 1: good agreement for AP‐PA fields; discrepancy of 7% for the lateral fields. Global differences (plans 1–3): about 4%, showing a compensating effect of the individual differences.P2: Global difference (plan 4): 15 %. This represents the worst case situation as it is a point surrounded by lung tissue, where the DC pencil beam algorithm is expected to give the greater difference against Acuros.Lung patients: Mean point difference inside the PTV:(5.4±4.2) %. Gamma passing rate inside the PTV:(45±12) %.Conclusion:The performance of DC in heterogeneous lung medium was studied with a special phantom and the results for 15 patients were analysed. The found deviations show that even though DC is a highly promising in vivo dosimetry tool, there is a need of incorporating a more accurate algorithm mainly for plans with low density regions involved.

SU-E-T-609: Evaluation of Transit Dosimetry Software Using Heterogeneous Phantom

Purpose: The purpose of this work was to evaluate limits and capabilities in the transit dosimetry software for use with the TomoTherapy system by irradiating a heterogeneous phantom. Methods: Helical TomoTherapy plan was created using CIRS phantom (model 062M) with nine various tissue equivalent inserts (lung inhale 0.2 g/cm3, lung exhale 0.5 g/cm3, adipose 0.96 g/cm3, breast 0.99 g/cm3, water 1.01 g/cm3, muscle 1.06 g/cm3, liver 1.07 g/cm3, trabecular bone 1.16 g/cm3, and dense bone 1.53 g/cm3). Targets were contoured within every insert. The phantom was scanned with a 50 cm field of view and 3 mm slice width. Images were imported into the TomoTherapy TPS. A plan was generated to deliver 20 Gy to every insert (2 Gy per fraction) with a jaw width of 2.5 cm, a pitch of 0.430 and an actual modulation factor of 2.621. After the radiation delivery the planning CT, the RT structure, the RT plan, and the RT dose (DICOM format) as well as the exit detector sinogram were imported into the Dosimetry Check software (Math Resolutions, LLC). The 3D delivered doses were reconstructed from the exit detector data by correcting for phantom and couch attenuation. The resulting dose distribution were compared with the TPS planned dose using gamma index. Results: Using the clinical gamma criteria, 3% and 3 mm, all tissue equivalent inserts had a passing percentage of 100% except for 0.2 g/cm3 and 0.5 g/cm3 density inserts (gamma value of 81.67% and 99.18% respectively). Conclusion: The evaluated transit dosimetry software provides an independent verification of helical TomoTherapy plans giving additional confidence in the treatment delivery, however, an overestimation of the reconstructed dose in low density materials has been revealed. Implementation of Monte Carlo algorithm for exit dose reconstruction should improve dosimetric accuracy in heterogeneous patient tissues. Agreement with Math Resolutions

Pre-treatment and in-vivo dosimetry of Helical Tomotherapy treatmentplans using the Dosimetry Check system

Dosimetry Check (DC) is the world's first commercially availablesoftware that provides patient-specific pre-treatment (PTD) and in-vivotransit (IVD) dose quality assurance of static and rotationalintensity-modulated radiotherapy treatments. To investigate the feasibilityof replacing pre-treatment verification with in vivo dosimetry for HelicalTomotherapy (HT), the commissioning and the application of the DC softwarewas realised. Dose distributions were reconstructed from Mega VoltageComputed Tomography (MVCT) detectors, inside phantoms or patients for atotal number of 6 treatment plans. Planned, reconstructed MVCT dose andmeasurements using ionisation chambers and a matrix detector inserted incylindrical and octagonal phantoms, respectively, were compared at theisocenter and in two dimensions using the γ2D and γ10-index (3% / 3 mm). The dose reconstruction PTD and IVD methodsof DC software provided, compared to detector measurements and for threeQuality Assurance (QA) plans, similar point dose deviations and γ2D-index passing rates: (0.4 ± 0.1)% vs. (-1.4 ±1.6)%, and (96.8 ± 0.9)% vs. (98.9 ± 0.6)%, respectively.In terms of γ10-index passing rate, PTD and IVD modalitiesreached mean values of (99.3 ± 0.1)% and (97.2 ± 1.9)%,respectively. Also for the remaining three clinical plans, similar resultswere reached for IVD with γ10-index passing rate reaching meanvalues of (95.9 ± 3.4)%. Therefore, either the PTD and the IVDverification modalities proved to be a very promising tool for thepatient-specific QA of HT Plans.

Clinical implementation of ‘Dosimetry Check’ for patient in vivo dosimetry using transit electronic portal images acquired during treatment

‘Dosimetry Check’ (DC) (Math Resolutions LLC) was implemented across 12 linacs at Clatterbridge Cancer Centre: 8 Varian and 4 Elekta. The system was commissioned to perform in vivo dosimetry measurements using transit electronic portal images (EPIs) acquired during patient treatments. Commissioning required between 2 and 5 hours per linac and involved acquiring a series of EPIs at each available energy through different depths of water then fitting dose deconvolution kernels to the signal measured on the central axis of each image. Validation was performed by delivering a series of increasingly complex, clinically representative test plans to phantoms. Across all linacs and validation plans the DC dose measurements were in excellent agreement with TPS calculations: Varian m=0.0% σ=0.5%; Elekta m=0.0 σ=1.0%. To date over 1000 actual patient treatments have been verified using in vivo transit dosimetry, including conformal and VMAT treatments across a range of anatomical sites. Agreement at the prescription point was within 7% in 95% of cases, with most outliers explainable by changes in patient shape or incorrect alignment of the portal imaging device. Performing these measurements caused no increase in the duration of the treatment appointment. Radiographer and physics training programmes have been developed and staff acceptance of the new technology has been high. DC is a robust and efficient platform for in vivo dosimetry which imposes a minimal burden on treatment staff yet has the advantage of providing volumetric dose delivery information. Its applications in pre-treatment IMRT QA and adaptive radiotherapy are currently being explored.

SU‐E‐T‐176: Commissiong and Initial Clinical Experience with Dosimetry Check, a Commercial Software for in Vivo Volumetric Dosimetry

Purpose: The aim of this work is to study the differences of reference point doses between the commercial EPID based dosimetry software Dosimetry Check (DC) and TPS to establish an accuracy level of the system, to evaluate its use in clinical routine and to obtain results for the first patients. Methods: We used DC v.3.8 (Math Resolutions), two Varian Clinac iX accelerators equipped with EPID aS1000 and Eclipse v.10.0 with AAA algorithm. Several plans with and without air gap were generated over the phantoms: MP1 Water Tank and Solid Octavius 4D (PTW). 5 head and neck, 3 lung and 4 prostate cases were selected for clinical evaluation. We compared the calculated dose at the isocenter and in a set of 9 points distributed in the PTV and made a gamma analysis of the 3D volume in pre‐treatment mode and during 3 CBCT‐guided sessions in transit mode. Results: In the study with phantoms, total dose differences in the isocenter between DC and TPS are less than 2%, but single field contributions achieve greater values. In transit mode, DC does not consider properly the couch attenuation, especially when there is an air gap between phantom and couch. For patients, better results are observed for prostate than for lung (heterogeneities) or head and neck (heterogeneities, field size). Information is lost in edges of large fields due to the limitation in EPID size and in the event of an interruption during treatment. Conclusion: Tests carried out with phantoms suggest that the accuracy of DC achieves 2% for total dose. For off‐axis dose distribution, and also for patients, this uncertainty results significantly higher. In any case, the possibility of this in vivo evaluation and the potentiality of this new system have a very positive impact on improving patient QA.

Evaluation of a new 3D in vivo dosimetry software using portal imaging for VMAT treatments of prostate: Preliminary results

Introduction/Objectives The control of VMAT treatments is a key issue in the Quality Assurance process. Current solutions are often cumbersome to implement and unsuitable for routine use. An innovative solution is proposed by the Dosimetry Check software (Math- Resolutions) allowing both to control pre-treatment as well as socalled transit dosimetry using the portal imager. Here we present the implementation and the evaluation of the software to control VMAT treatments of prostate. Material and methods Acquisition where made on a Clinac 2100C equipped with an IaS500. Images, acquired in continuous mode (@60 frames/rotation), CT scanner and associated structures and 3D dose matrix are imported in Dosimetry Check. Fluence matrix in air is obtained by filtered backprojection. The dose volume in the patient is calculated with Pencil Beam algorithm. Analysis is based on the comparison of point dose, dose profiles, and dose distributions in 2D and 3D. The calculation of Dose Volume Histogram and Gamma Index is also available. Results and conclusion The study focuses on 10 cases of prostate cancer treated in VMAT according to simultaneous integrated boost. The deviation of measured dose at the isocenter in pre-treatment and in transit mode is of the order of −4.0%(±1.3%) and 4.9%(±4.1%) respectively. These results improve significantly when corrected by the acquisition of an integrated image: +1.4%(±0.7%) in pre-treatment and −1.1%(±0.7%) in transit mode. Dosimetry Check software is a suitable tool to do pre-treatment control and in vivo dosimetry. The first results are satisfactory and we wish to test it on other sites, but weaknesses of Pencil Beam algorithm have to be taken into account.

SU-E-T-26: Evaluation of New Pre-Treatment In-Air Patient Specific QA Software for TomoTherapy Treatments.

Math Resolutions, LLC, has extended their Dosimetry Check quality assurance software to include TomoTherapy treatments. Data collected from TomoTherapy's MVCT detectors is processed and compared to the planned treatment dose allowing for pre-treatment QA without the use of phantoms and other detectors. This study presents an overview of our experience at the University of Virginia developing, implementing, and verifying this novel QA strategy. Low modulation and high modulation cheese phantom plans as well as patient plans (prostate, GYN, and vertebra) were used to test the Dosimetry Check in-air software. For all evaluations the treatment table was removed from the XML file of each plan using software provided by Accuray and the resulting in-air calibration plan was delivered. The exit detector sinogram was extracted from the machine and imported into Dosimetry Check along with the TomoTherapy calculated planned dose. The fluence maps were reconstructed and used to recalculate the dose. The percent difference between the planned dose and the dose calculated from the exit detectors by Dosimetry Check ranged between 0.62% for a simple low modulation cheese phantom plan with a cylindrical target to 7.3% for a high modulation 2.5cm prostate plan. The gamma indices reported range from 94.7% to 97.8% <1 over the overall calculation area for the plans tested using a gamma of 3% and 3mm. For the area receiving over 80% of the prescribed dose, the gamma ranged from 80.7% to 92.9% <1. The results of our investigation of Math Resolutions' new product in development, Dosimetry Check's pre-treatment in-air QA software, demonstrate that it has the potential be a very useful and practical tool for TomoTherapy QA. Further testing is being performed in which various errors are intentionally introduced in the delivered dose to test the limits of Dosimetry Check's sensitivity. Research Grant from Math Resolutions LLC 01/12/2012-01/11/2013 Math Resolutions’ Dosimetry Check software was given to UVa to assist with evaluating the precision of the product in reconstructing dose from the TomoTherapy exit detector data.

SU-D-BRCD-05: Evaluation of New Exit Detector Based Transit Dosimetry Software for TomoTherapy Treatments.

The prospect of 3D transit dosimetry to verify treatment delivery is a novel and emerging technology in TomoTherapy. Math Resolutions, LLC, has expanded their Dosimetry Check (DC) quality control software to include transit dosimetry calculations for TomoTherapy treatments. The data recorded by the MVCT detectors during patient treatment is used in conjunction with the planning CT to calculate the delivered dose to the patient from each fraction. This study presents a summation of our experiences at the University of Virginia in collaboration with Math Resolutions in verifying and implementing the transit-dose calculation aspects of this new TomoTherapy specific product. Low and high modulation cheese phantom plans and clinical plans (prostate, GYN, pituitary, and thoracic vertebra) were used to evaluate the DC transit dosimetry software. The TomoTherapy planning CT, structure set, plan, and dose for each plan were imported into the DC software. The fluence maps were reconstructed from the exit detector data by correcting for patient attenuation and used to compute the delivered dose. The resulting dose distribution is compared with the TPS planned dose using isodose line comparison and gamma index. The percent difference between the planned and DC calculated doses ranged between 0.63% for a low modulation cheese phantom plan to 5.94% for a prostate plan. Using criteria of 3%, 3mm, the gamma index passing rate for the tested plans ranged from 94.7% to 99.1% <1 for the overall patient area and from 88% to 96.4% for the treatment area receiving at least 80% of the prescribed dose. The results from our evaluation of Math Resolutions' DC look promising and generally within an acceptable range for portal dosimetry programs. Further investigations will include developments to improve the DC algorithm and determine how it can best be implemented in a typical TomoTherapy clinical workflow. Research Grant from Math Resolutions LLC 01/12/2012-01/11/2013 Math Resolutions™ Dosimetry Checksoftware was given to UVa to assist with evaluating the precision of the product in reconstructing dose from the TomoTherapy exit detector data.